全文获取类型
收费全文 | 215513篇 |
免费 | 2229篇 |
国内免费 | 649篇 |
专业分类
化学 | 110528篇 |
晶体学 | 3377篇 |
力学 | 9577篇 |
综合类 | 5篇 |
数学 | 24294篇 |
物理学 | 70610篇 |
出版年
2021年 | 1842篇 |
2020年 | 2061篇 |
2019年 | 2292篇 |
2018年 | 2836篇 |
2017年 | 2761篇 |
2016年 | 4184篇 |
2015年 | 2753篇 |
2014年 | 4076篇 |
2013年 | 9708篇 |
2012年 | 8113篇 |
2011年 | 9606篇 |
2010年 | 6596篇 |
2009年 | 6384篇 |
2008年 | 8608篇 |
2007年 | 8756篇 |
2006年 | 8341篇 |
2005年 | 7487篇 |
2004年 | 6903篇 |
2003年 | 6035篇 |
2002年 | 5865篇 |
2001年 | 6601篇 |
2000年 | 5080篇 |
1999年 | 3934篇 |
1998年 | 3186篇 |
1997年 | 3184篇 |
1996年 | 2909篇 |
1995年 | 2700篇 |
1994年 | 2545篇 |
1993年 | 2430篇 |
1992年 | 2760篇 |
1991年 | 2735篇 |
1990年 | 2651篇 |
1989年 | 2463篇 |
1988年 | 2498篇 |
1987年 | 2483篇 |
1986年 | 2316篇 |
1985年 | 3015篇 |
1984年 | 3258篇 |
1983年 | 2675篇 |
1982年 | 2847篇 |
1981年 | 2820篇 |
1980年 | 2681篇 |
1979年 | 2766篇 |
1978年 | 2864篇 |
1977年 | 2857篇 |
1976年 | 2933篇 |
1975年 | 2704篇 |
1974年 | 2667篇 |
1973年 | 2807篇 |
1972年 | 1784篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
911.
Kochina T. A. Vrazhnov D. V. Sinotova E. N. Shishigin E. A. 《Russian Journal of General Chemistry》2004,74(2):193-196
Reactions of diethylsilylium ions with dibutyl ether in the gas and liquid phases were studied radiochemically. These reactions, as those with benzene and alcohols, are accompanied by partial rearrangement of diethylsilylium ions into monoethylsilylium and dimethylsilylium ions. The extent of transformations of the (C2H5)2SiT+ ions decreases in going from benzene to dibutyl ether, which is due to the higher energy of adduct formation with the ether, compared to benzene. 相似文献
912.
This work shows that nuclear data and neutron flux parameters can be applied to calculate directly the elemental concentrations.
Techniques for extracting neutron flux parameters pertaining to the irradiation positions and nuclear data pertaining to the
isotopes concerned from measured reaction rates have been previously developed. This method is compared to the comparator
and relative methods of activation analysis. The principles, advantages and disadvantages of each method and sources of errors
are discussed. It also briefly discusses other factors such as accuracy and precision, sensitivity, detection limits and limit
of quantitative determination. The three methods are applied to the analysis of five environmental reference materials. The
concentrations of more than 20 elements are determined. The results show a good agreement with the certified and/or literature
values. 相似文献
913.
The double-T injector design employed in many microchip capillary electrophoresis devices allows for the formation of very small (50-500 pL) sample plugs for subsequent analysis on-chip. In this study, we show that sample plugs formed at the channel junction can be geometrically defined. The channel width and injector symmetry prove to be of great importance to good performance. A unique pushback of solvent into the side channels can be induced when the side channels have a very low resistance to flow, and this helps to better define the injected sample plug. Samples and running buffers of differing ionic strength (e.g., 10 mM KCl buffer and 20 mM KCl sample) can yield widely variable results in terms of plug shape and amount injected (variations of 1.5 to 10x). Applying bias voltages to all the intersecting channels aids in controlling the plug shape. However, when the ionic strengths of buffer and sample are not matched, the actual amount injected (up to 10x variations) can be inconsistent with the appearance of the plug formed in the injector (up to only 30 % variations). Operating at constant pH and ionic strength produced the most consistent results. This report examines the effects of altering the injector geometry and solution ionic strengths, and presents the results of using bias voltages to control plug formation. The observed results should provide a benchmark for modeling of the fluid dynamics in channel intersections. 相似文献
914.
Three multivariate techniques (principal components analysis, correspondence factor analysis and spectral map analsis) are applied to x-ray fluorescence data from glass-making objects from the 5th century AD found in Tarragona (Tarraco in the Roman Empire). The information obtained by displaying th eobjects and variables in each reduced factor space is compared. The presence of redundant information is shown. The visualization of groups of objects and of the relationship between objects and variables allows the formulation of hypotheses concerning the origin of the samples and the presence of local glassworks. 相似文献
915.
B. V. Potapkin M. A. Deminsky A. A. Fridman V. D. Rusanov 《Radiation Physics and Chemistry》1995,45(6):1081-1088
Theoretical investigation of the effect of molecular clusters and aerosol particles on non-equilibrium plasma flue gas cleaning was made in this paper. Two types of heterogeneous reactions in aerosol and clusters are considered. It was shown that in both cases these reactions are essential in the evaluation of chemical composition. As a result of theoretical approach and modelling, the optimum regime of plasma generation for essential decreasing of purification energy cost was established. 相似文献
916.
T. A. Kochina D. V. Vrazhnov I. S. Ignat'ev E. N. Sinotova 《Russian Journal of General Chemistry》2003,73(1):61-65
Radiochemistry was used to study reaction of tritium-labeled diethylsilylium ions with alcohols in the gas phase. The reaction involves both rearrangement of the diethylsilylium ions and isomerization of the substituent in the substrate. The hydroxyl hydrogen of the alcohol and the tritium atom of the diethyl-silylium ion undergo exchange which, however, is less vigorous that in the case of the monoethylsilylium ion. A possible reaction mechanism is proposed. 相似文献
917.
N. V. Vasil'ev V. M. Koshelev D. V. Romanov K. A. Lyssenko M. Yu. Antipin G. V. Zatonskii 《Russian Chemical Bulletin》2005,54(7):1680-1685
Cycloaddition reactions of polyfluorinated 1,3-oxazoles with cyclic and acyclic alkenes were studied. The results of these
reactions were interpreted using quantum chemical calculations. An unusual product, viz., fluorine-containing acylpyrrole, was studied by X-ray diffraction.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1630–1635, July, 2005. 相似文献
918.
919.
Fusicoccin A has been isolated from a culture filtrate of the filtrate of the fungusFusicoccum amygdali Del., and it has been characterized as an -glycoside of a tricyclic diterpenoid. The trimethylsilyl derivative of fusicoccin A has been investigated by combined GLC and mass spectrometry.All-Union Scientific-Research Institute of Applied Biology and Genetics, VASKhNIL, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 792–796, November–December, 1980. 相似文献
920.
The oxidation of 2,6-dichloro-3-benzylpyridines and bis(2,6-dichloro-3-pyridyl)methanes, respectively, was accomplished using chromic trioxide in a highly acidic medium. The synthesis of several phenyl-3-(2,6-dichloropyridyl)ketones and of bis(2,6-dichloro-3-pyridyl)ketone are reported. 相似文献